1. Field of the Invention
The present invention relates to a process for transmitting items of information between devices of an indirectly controlled exchange system, and is more particularly concerned with the transmission of information between devices of an indirectly controlled telephone exchange system.
2. Description of the Prior Art
It is well known in the art to detect alterations in the operating state of associated devices in exchange systems in order to be able to perform allied switching procedures. This involves the use, for example, of items of interrogation information which are then compared with earlier items of interrogation information emanating from the same device, for analysis purposes. In dependence upon the comparison results, operating procedures are carried out in the exchange system (see German published application Nos. 14 37 576 and 23 17 400; German Pat. No. 12 13 008; and German patent application No. P 27 44 118). In exchange systems of this kind, the interrogation of the device is directly linked to the analysis of the interrogation information which is obtained, and therefore between the interrogation of two different devices the comparison of second items of interrogation information of the same device is carried out, which may possibly be followed by the storage of the address of a device in respect of which the operating state has changed, which has resulted from modified interrogation information (see German Pat. No. 12 13 008). Also known in the art is the possibility of interrupting the interrogation process in order to perform the required operating processes which result from the obtained interrogation information (see the German allowed application No. 14 37 576, Page 74).
In this known technology it is provided that further processing on the basis of items of interrogation information in the control unit be carried out only when it is a question of modified information. Technology of this kind has already been proposed for an indirectly controlled exchange system which comprises a control unit for which items of information emanating from a plurality of other devices are regularly recorded at specific intervals of time for further processing, for which purpose the items of information are first stored, whereupon consecutive items of information emanating from the same device are compared with one another before items of information are further processed by the control unit on the basis of information modifications (see German patent application No. P 28 34 938). This can also take place in a telephone exchange system which is equipped with time channel couplers and wherein items of communication to be exchanged between subscribers are transmitted in pulse code modulation (PCM) operation by way of time division multiplex (TDM) channels.
However, it is also possible in an exchange system of this kind that items of information which are identical in content may have to be transmitted at longer or shorter intervals of time, where, in spite of their conformity, each of these items of information which are to be transmitted must trigger a processing procedure. These items of information can consist, for example, of test commands which are transmitted from a central control device to a peripheral device. If test commands of this kind are transmitted, for example, at a time of day at which very low traffic prevails, it is likely that, in spite of a certain interval of time between such test commands, they will not be altered by other items of information to be transmitted. The later test command which conforms in content with the previous, is, however, to initiate the commanded test. Test commands of this kind must be transmitted, for example, from a central control device to a peripheral device in the exchange system. The information can also consist for example, of items of dialled information which are identical in content, since they relate to two dialled digits, which are dialled consecutively by a subscriber and which are identical. Items of dialled information of this kind must be transmitted, for example, from peripheral devices to a central control device. In this case, each digit transmitted as a result of an item of dialled information must be analyzed as a separate dialled digit in the control device.